1. Field of the Invention
The present invention is directed to a vanadium/phosphorus oxide catalyst, method of preparation of such catalyst, and the use of the catalyst in the production of maleic anhydride.
2. Background of the Invention
Maleic anhydride may be used as a raw material in the production of many products, such as synthetic resins, and may generally be prepared by the catalytic oxidation of n-butane. The catalyst of choice for this oxidation is typically a catalyst containing vanadium, phosphorus, oxygen (VPO), and optionally a promoter component.
These VPO catalysts are generally prepared by contacting vanadium-containing compounds with phosphorus-containing compounds and optionally promoter component containing-compounds under conditions suitable to reduce the pentavalent vanadium to the tetravalent state to thereby form a catalyst precursor containing vanadyl hydrogen phosphate and optionally the promoter component. The catalyst precursor may then be recovered and typically formed into a shaped body, such as a tablet or pellet, by compression in a die. A lubricant is ordinarily incorporated as well to aid in the tableting or pelleting process. The pellet or tablet may then be subjected to calcination to transform the catalyst precursor into an active catalyst containing vanadyl pyrophosphate.
In addition to promoter components, VPO catalysts may be prepared by further adding high vapor pressure additives to control the pore structure of the catalyst as disclosed in U.S. Pat. No. 5,275,996, which is incorporated by reference herein in its entirety. Additives disclosed in this reference include polyethylene oxide, adipic acid, citric acid, oxalic acid, stearic acid, palmitic acid, lauric acid, myristic acid, esters of such acids, naphthalene, polyethylene glycol, polyvinyl alcohol, polyacrylic acid, cellulosic materials, monosaccharides, polysaccharides, hydrogenated vegetable oils, waxes, and gelatin. One drawback to the use of these additives is that the additives are removed from the catalyst by heat treatment at elevated temperatures, typically with the use of a stripping gas, which can deactivate the catalyst, cause overstripping or dehydration and reduce productivity of the catalyst due to increased processing time and rigorous control needed in handling a flammable material at elevated temperatures.
Thus, efforts are continually being made to define new and improved VPO catalysts and methods and processes of making new and old VPO catalysts in order to reduce cost and/or upgrade the activity, selectivity, and productivity of such catalysts.